Edexcel IGCSE Chemistry 4.33C fermentation conditions

Practise fermentation-condition questions by linking absence of air to ethanol yield and temperature to enzyme activity.

Exam points

Explain why air is excluded so ethanol is not oxidised to ethanoic acid.
Link 30-40 °C to enzyme activity, including slow rates and denaturation above 40 °C.

[Maximum number: 2]

Some cars in Brazil use ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}$ , as a fuel instead of petrol.
The ethanol is made by the fermentation of glucose which is obtained from sugar cane.
The sugar is extracted from the sugar cane and then dissolved in water to make a sugar solution.

Explain why fermentation is done in the absence of air.

An explanation using either of the following linked pairs:

M1 oxygen in the air would react with ethanol

M2 to form ethanoic acid

OR

M1 the fermentation/reaction/respiration needs to be anaerobic

M2 ethanol would not be formed / $\mathrm{CO}_{2}$ and $\mathrm{H}_{2} \mathrm{O}$ would form

ACCEPT ethanol would be oxidised

ALLOW to form carboxylic acid

ALLOW to form vinegar

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4.33C Fermentation conditions question 1